I don't really know much about history of this design, except that it is
a French Army 1952 model, probably inspired by a British Pattern 37 mess kit instead of classical pot-and-pan design. French mess tin consists of three rectangular, thick aluminum pans with rounded corners, stowed into each other.
Downside of this solution is lack of the large main pot to be hanged over the campfire.In return you get a handy, compact design, better suited to fit into a rucksack, side pocket of a backpack, belt pouch or even cargo pocked on your fatigues than it's kidney-shaped counterpart.